Effects Of The Different Grazing Systems On Vegetation And Soil Of Stipa Breviflora Desert Steppe

Effects of rotational and continuous grazing on plant population,community and soil characteristics of Stipa breviflora desert steppe were investigated during 2005-2007 year.The main results were shown as follows:1 Grazing decreased the height of Stipa breviflora and Cleistogenes songorica;the coverage,the density,the importance value of Cleistogenes songorica and Allium polyrhizum in rotational grazing were higher than those in continuous grazing,which of Stipa breviflora in continuous grazing were higher than those in rotational grazing.Banning and rotational grazing were beneficial to increase the above-ground standing crop and the relative standing crop of Cleistogenes songorica and Allium polyrhizum.Continuous grazing was beneficial to increase the above-ground standing crop and the relative standing crop of Stipa breviflora.2 Banning and rotational grazing improved plant growth and sexual reproduction; Rotational grazing increased tiller nodes biomass of Allium polyrhizum,energy of standing crop and total standing crop of population modulus of Stipa breviflora and Allium polyrhizum.The root biomass,energy of standing crop and the ratio of their allocation,and ratio of root to crown of the main plant populations in the two grazing systems were higher than those in ungrazed pasture.The calorific value of different modulus among major plant population and whole plants in rotational grazing were higher than that in continuous grazing.There were no significant trade-off between vegetative and reproductive shoot biomass/energy,but trade-off between tiller nodes and vegetative shoot biomass/energy was observed.3 The double-peaks on the curves of diurnal changes of photosynthetic rates, transpiration rates and stomatal conductance of Stipa breviflora,Cleistogenes songorica and Allium polyrhizum were observed,and there was distinct phenomenon of"noon break".The double-valley on the curves of diurnal changes of internal CO2 concentration was observed.Rotational grazing increased the photosynthetic rates,transpiration rates,stomatal conductance and internal CO2 concentration of the major plant populations on desert steppe.Photosynthetic response of Stipa breviflora,Cleistogenes songorica and Allium polyrhizum to Photosynthetically active Radiation(PAR) in the different treatment were"parabola"type.Photosynthetic response curves of the same plant to PAR were that banning grazing area was higher than rotational grazing area,in turn,higher than continuous grazing area.There were significant positive correlation between the photosynthesis rates,transpiration rate and stomatal conductance and PAR of the main plant populations under the different treatments.The trend of internal CO2 concentration was slightly decreasing with the increase of PAR,which was quadratic polynomial equation expressed on PAR.4 The trends of density and coverage of Stipa breviflora were decrease,and the rate of decline in rotational grazing was light.The trends of density of Cleistogenes songorica and Allium polyrhizum were increase in rotational and banning grazing area.The trend of coverage of Allium polyrhizum was increase in banning grazing area.The total coverage of community in rotational grazing area was 1.83 times of that in continuous grazing area. The important values of Stipa breviflora,Cleistogenes songorica,Allium polyrhizum, Cleistogenes squarrosa,Allium tenuissimum and Convolvulus ammannii in rotational and banning grazing area were high.However,annuals plants played an important role in continuous grazing area.The important value of Artemisia frigida in continuous grazing area was increase;important value of Asparagus gobicus (a high drought resistant plant) was stable;important value of Lagochilus ilicifolius was significant increase.From the view of the important values,the continuous grazing area was considered an indication of grassland degeneration and inhabit dehydration.5 The indexes of Margalef richness,Shannon-Wiener diversity and Simpson diversity were shown that rotational grazing area was higher than continuous grazing area,in turn, higher than banning grazing area.Pielou uniformity index in the banning grazing area was higher than that in the rotational and continuous grazing area.Four diversity indexes in the different treatment were increase,which were high in rotational grazing area.The correlation between Shannon-Wiener index,Simpson index and Margalef richness index were higher than that between Shannon-Wiener diversity index,Simpson diversity index and Pielou Uniformity index.The index ofβ-diversity of community decreased with the increase of quadrat size.The index ofβ-diversity of desert steppe was high in rotational grazing area.The Morisita-Horn similarity coefficient of in the banning and in the rotational grazing area are high,which was 0.884.The Morisita-Horn similarity coefficient in the different treatments were a declining trend.6 The plant aboveground standing crop in rotational and banning grazing were higher than that in continuous grazing,and increased by 2.87 times and 0.57 times, respectively, than that in continuous grazing.The underground biomass declined with increase of soil layers deeper in different treatments,which showed"T"type,and was accordant to the declining pattern depicted by the exponential function;The biomass of root increased with the trend of distribution in surface soil.The trend of root upward movement in rotational grazing area were lower than that in continuous grazing area.Rotational grazing area increased plant species of seed bank of grassland community and the species type of fine grasses.The density of soil seed bank in banning grazing area were significantly higher than that in rotational and continuous grazing area.The soil seed bank declined when their soil layers became deeper in different treatments,which of 75.06 to 83.19% was distuibuted in the 0~5cm soil layer,14.16 to 21.68% in the 5~10cm soil layer,2.65 to 4.90% in the 10~15cm soil layer.Margalef index and Shannon-Wiener index of soil seed bank in rotational grazing area were higher than that in continuous grazing area.The Morisita-Horn similarity coefficient of soil seed bank in the banning and in the rotational grazing area were the high.7 The proportions of silt and clay particle in rotational and banning grazing were higher than that in continuous grazing,whereas the proportions of sandy particles in them were lower than in continuous grazing.Rotational grazing area decreased soil bulk, increased soil porosity and soil water content.Rotational and banning grazing also increased the contents of organic matter,the contents of N,total K and available K.The contents of P of soil upper layer,pH in rotational grazing were the high.Grazing reduced the ratio of carbon to nitrogen.The fitting curve was quadratic power function between soil nutritent content and depth of soil.8 There was a positive correlation between the above-ground standing crop and soil water content.The fitting curve was quadratic equation between soil water content and species diversity index of above-ground vegetation under different grazing systems in desert steppe.There were significant positive correlations between soil water content and Margalef richness index,Shannon-Wiener diversity index in rotational grazing area,which were 0.8186 and 0.6496,respectively.This showed different effect of different grazing systems on the soil physical and chemical properties indicators.The relationship of soil indicators under different treatments were also different.There was high correlation between the basal composition and nutrient of soil,and the relationship of soil nutrient in rotational and banning grazing area were higher than that in continuous grazing area.